That's the point - the op doesn't have a vfd, just a phase converter. I would suggest again, a bigger inverter with low speed torque boost would fix this, and also make sure the motor is delta wired. In fact I would delta wire the motor first, then get a vfd if the converter fails to move it.
I think I have a knacked one here somewhere too. Is that a zenon tube on it? From memory they used an inverter and charged a capacitor with a thyristor or similar switch. Should make a high pitched low volume whine.
Indeed, you're right. Look for a used Centec, preferably with a vertical and horizontal attatchment - they do come up, one or two people on here have them.
There you go, rewire it between the bottom right pin and the top left. And make the earth longer. And change the plug. You may have to change the flex too, if it's 2.5mm it's limited to 20A I think?